As used herein, “intangible goods” is a generic label for electronically stored or transmitted content. Examples of intangible goods include images, audio clips, video, multimedia, software, metadata, and data. An intangible good may be analog or digital. Depending upon the context, an intangible goods may also be called a “digital signal,” “content signal,” “digital bitstream,” “media signal,” “digital object,” “object,” and the like.
Intangible goods are often distributed to consumers over private and public networks—such as Intranets and the Internet. In addition, these goods are distributed to consumers via fixed processor-readable media, such as a compact disc (CD-ROM), digital versatile disc (DVD), soft magnetic diskette, hard magnetic disk (e.g., a preloaded hard drive), portable media players, and flash memory cards. Furthermore, goods are distributed via communications streams such as those originating from a client such as an instant messenger or another audio/visual chat application.
Unfortunately, it is relatively easy for a person to pirate the content of intangible goods at the expense and harm of the content owners—which include the content author, publisher, developer, distributor, etc. The content-based industries (e.g., entertainment, software, audio and/or video, film, etc.) that produce and distribute content are plagued by lost revenues due to piracy.
Embedded-Signals
Embedding one or more signals in a carrier signal (e.g., intangible goods) is one of the most promising techniques for protecting the content owner's rights of intangible goods. This embedded-signal is commonly called a “watermark” and the embedding process is commonly called “watermarking.”
Generally, watermarking is a process of altering the intangible good such that its perceptual characteristics are preserved. For example, a “watermark” is a pattern of bits or signal stream inserted into a digital or analog good that may be used for many purposes, such as identifying the content owners and/or the protected rights.
A watermark embedder (i.e., encoder) is used to embed a watermark into intangible goods. A watermark detector is used to detect the existence of the watermark in the watermarked intangible goods and possibly identifying that watermark.
Watermark detection is often performed in real-time even on small electronic components. Such a “real-time” detector is also often called a “dynamic detector.” Generally, this means that the detector is attempting to detect a watermark in intangible goods as the goods are being consumed (e.g., played, presented, stored, and such). For example, if the intangible good is an audio signal, the detector attempts detection while the audio signal is being played. If, for example, the intangible good is a video signal, the detector attempts detection while the video signal is being played.
Such dynamic watermark detection is often a very expensive operation (in terms of computing resources). If there are multiple input streams, then conventionally there are multiple dynamic watermark detection modules running (i.e. one per input stream). The expense in computing resources increases with each watermark detection module invoked to operate on an input stream.
Those of ordinary skill in the art are familiar with conventional techniques and technology associated with watermarks, watermark embedding, and watermark detecting.
Common Attacks
A watermark is typically designed to survive a wide variety of signal processing, (e.g., compression, equalization, D/A and A/D conversion, recording on analog tape, color correction, and so forth). It is also typically designed to survive malicious attacks that attempt to remove the watermark or obscure it (e.g., changes in time and frequency scales, pitch shifting, and cut/paste editing).
Unlike a physical watermark in paper, a digital watermark in a digital picture, document, video, or audio signal is relatively easy to defeat. Many academic and research institutions have ascertained that watermarks can be easily removed from the content without much effort. The more robust a system is, the more susceptible it is to an attacker identifying the watermark within the content. Some basic attacks are:                Averaging. An averaging attack examines a large number of images or videos that use the same watermark for a similar detectable mark. The watermark appears as a common deviation across the images, which permits an attacker to extract the watermark from the files fairly accurately.        Surgical. A surgical attack uses exact prior knowledge of the watermarking algorithm and inner workings of the watermarking scheme to recover the original piece of content by removing only the part that represents the watermark. (It is possible to create a software crawler to automate this process.) The main advantage of such an attack is that it does not diminish the quality of the resulting content.        
Since the watermark is subject to both naturally occurring environmental factors and malicious attacks, the watermark embedding and detection process is typically designed to be resilient to attacks. This quality is often called “robustness.”
The standard set of example attacks is itemized in the Request for Proposals (RFP) of IFPI (International Federation of the Phonographic Industry) and RIAA (Recording Industry Association of America). The RFP encapsulates the following security requirements:                two successive D/A and A/D conversions,        data reduction coding techniques such as MP3 or WMA,        adaptive transform coding (ATRAC),        adaptive subband coding,        Digital Audio Broadcasting (DAB),        Dolby AC2 and AC3 systems,        applying additive or multiplicative noise,        applying a second Embedded Signal, using the same system, to a single program fragment,        frequency response distortion corresponding to normal analogue frequency response controls such as bass, mid and treble controls, with maximum variation of 15 dB with respect to the original signal, and        applying frequency notches with possible frequency hopping.        